Generation of 131 fs mode-locked pulses from 2.8μm Er:ZBLAN fiber laser

We demonstrated a femtosecond mode-locked Er:Zr F4-Ba F2-La F3-Al F3-Na F(Er:ZBLAN)fiber laser at 2.8μm based on the nonlinear polarization rotation technique.The laser generated an average output power of 317 m W with a repetition rate of 107 MHz and pulse duration as short as 131 fs.To the best of our knowledge,this is the shortest pulse generated directly from a mid-infrared mode-locked Er:ZBLAN fiber laser to date.Numerical simulation and experimental results confirm that reducing the gain fiber length is an effective way to shorten the mode-locked pulse duration in the Er:ZBLAN fiber laser.The work takes an important step towards sub-100-fs mid-infrared pulse generation from mode-locked Er:ZBLAN fiber lasers.     

皮秒拍瓦激光的参数测量系统可靠性分析

皮秒参数测量系统用于提供皮秒拍瓦激光系统的各项状态参数,协助激光系统达到预期的技术指标。针对皮秒拍瓦激光系统的技术指标,皮秒参数测量系统将提供压缩脉冲的能量、脉宽、远场、信噪比等参数。为了判断参数测量系统的工作性能,采用均方根(RMS)误差来描述测量系统的可靠性。经过实验测试,能量测量单元的测量范围为10～1000J,标定实验数据的RMS误差为2.2%。脉宽测量单元的时间测量范围为0.5～18.0ps,时间分辨率为0.07ps,测试数据的RMS误差为3%。远场测量单元的空间测量范围为150倍衍射极限(DL),空间分辨率为0.3倍DL,测试数据的RMS误差为0.15%。信噪比测量单元的时间测量范围为30ps,时间分辨率为0.3ps,动态范围为106。基于拍瓦实验提供的测试数据表明,皮秒参数测量系统能够稳定可靠地提供以上参数的实时测试数据,实现拍瓦装置的运行状态诊断功能。     

浅谈中学数学课堂结构的改革

提高数学教学质量的关键在于提高课堂教学效率,而要提高课堂教学效率,其着眼点应放在改革课堂教学结构上,现就这个问题谈一点浅见。一、什么是课堂结构课堂结构是指课堂教学过程中各个环节的结合安排。就数学教学而言,如果把数学教学看成一个整体或母系统,那么它就有数学教学观、教材结构、教学方法,教师、学生、教学环境和设备等元件或子系统,这几个方面不是各自独立的,它们掺合在一起是立体的交叉的相互作用的。在课堂教学中,把这些元件组装起来,就形成课堂结构这部大机器。所以课堂     

2 μm mode-locking laser performances of sol-gel-fabricated large-core Tm-doped silica fiber

High-power ultrafast fiber lasers operating at the 2 μm wavelength are extremely desirable for material processing, laser surgery, and nonlinear optics. Here we fabricated large-core(LC) double-cladding Tm-doped silica fiber via the sol-gel method. The sol-gel-fabricated Tm-doped silica(SGTS) fiber had a large core diameter of 30 μm with a high refractive index homogeneity(Δn=2 × 10~(-4)). With the newly developed LC SGTS fiber as the gain fiber, high-power mode-locking was realized. By using a semiconductor saturable absorber mirror(SESAM) as a mode locker, the LC SGTS fiber oscillator generated mode-locked pulses with an average output power as high as 1.0 W and a pulse duration of 23.9 ps at the wavelength of 1955.0 nm. Our research results show that the self-developed LC Tm-doped silica fiber via the sol-gel method is a promising gain fiber for generating high-power ultrafast lasers in the 2 μm spectral region.     

基于光参量过程直接产生高重频超短脉冲序列

论证了单晶体光参量放大（OPA）过程在特定边界条件下满足频域宇称-时间（PT）反对称性。归一化的数值求解结果显示,OPA系统PT对称阈值点附近呈现增益跃变性质。对于存在位相失配的OPA,通过实时调控泵浦光强,即可控制系统PT对称性,论文基于相位失配OPA中可超快调控PT对称性的特性构建了超快光开关,一方面光开关与周期性幅度调制的泵浦光联合使用,可直接将连续激光转换为超短脉冲序列输出;另一方面,构建的光开关也可用于脉冲激光再压缩,有望用于中红外波等长波段超短种子源。论文提出的基于超快光开关直接产生超短脉冲序列的方案,由于不需要光学谐振腔,易于实现大于10 GHz的超高重复频率。     

Characterization and application of plasma mirror for ultra-intense femtosecond lasers

The femtosecond laser pulses reflected from the self-induced plasma mirror(PM) surface are characterized. More than two orders of magnitude improvement on intensity contrast both in nanosecond and picosecond temporal scales are measured. The far-field distribution, i.e., focusability, is measured to degrade in comparison with that without using a PM. Experiments on proton accelerations are performed to test the effect of the balance between degraded focusability and increased reflectivity. Our results show that PM is an effective and robust device to improve laser contrast for applications.     

皮秒自相关仪的性能测试研究

为了实现皮秒拍瓦激光的精密测试,研制了专用的皮秒自相关仪。选用无色散元件,提高了测量结果的可靠性。采用自标定方法标定时间分辨率,用超限法标定时间测量范围,用极值法标定脉冲响应特性。实验结果表明,皮秒自相关仪的时间分辨率为0.1ps/pixel,时间测量范围为26ps,脉冲响应特性的值为300fs。该皮秒自相关仪能够满足皮秒啁啾脉冲的时间宽度精密测试要求。     

产品可靠性(质量)综合评定

<正> 引言产品可靠性是产品本身具有的指标之一,任何产品都存在可靠性问题。本文只初步探讨电子设备这类产品可靠性的综合评定问题,但其评定方法也适用于其他产品。随着现代工业的兴起、发展和技术的迅